Cities across the state must slash water consumption by about 20 percent over the next decade under newly passed legislation aimed at reworking the aging policies and plumbing that determine water flow to 38 million Californians.

But the California agriculture industry, which consumes an estimated three-quarters of the water used in the state, won't have to change its practices much under the new rules.

And that vexes many involved in the political wrangling over water in a state where global warming, population growth and crumbling infrastructure are forcing wrenching changes in the way natural resources are divvied up.

"Water conservation targets are needed to make real progress and they have to happen among urban and agricultural interests - that's a huge missing piece when you think that agriculture is the largest water user in the state," said Juliet Christian-Smith, senior research fellow at the Pacific Institute, a nonpartisan water think tank in Oakland.

Gov. Arnold Schwarzenegger on Friday signed two of the five bills that make up the legislative package and is expected to sign the remaining three this week.

The legislation, which many observers tout as the biggest leap forward in water policy in a generation, calls for several meaty changes in the way the state oversees, stores and delivers water.

The package:

-- Creates a new oversight body for the ailing Sacramento-San Joaquin Delta, the hub of the state's water system.

-- Strengthens monitoring of the water pulled from underground aquifers.

-- Asks voters to approve an $11 billion-plus bond to pay for new dams and plumbing improvements.

-- Determines the minimum amount of water necessary to keep the delta ecosystem healthy.

-- Mandates that only urban users cut water use 20 percent by 2020.

It is the requirement that urban water users, but not agricultural interests, conserve that irks some observers.

With about 26 million acres in production and an economic output of some $36 billion, California's agriculture sector uses more than 75 percent of the water devoted to human use. It is also an industry criticized often for wasteful water use due in part to inexpensive, long-term water contracts, iron-clad water rights and federal subsidies that promote the growing of particularly thirsty crops, such as cotton and rice.

According to a Pacific Institute study released this summer, the state's farmers could save enough water each year using more efficient irrigation techniques to fill the Hetch Hetchy reservoir 16 times.

Some of those involved with the contentious debate over water policy in Sacramento wanted some recognition of those conclusions in the bills' language.

"There are (farming irrigation districts) that do a lot to stretch their water use - but we have to expand that to other agricultural water users," said Jim Metropolus, legislative representative at the Sierra Club. "Agriculture needs to do more."

Last year, Assemblyman Mike Feuer, D-Los Angeles, and then-Assemblyman John Laird, D-Santa Cruz, introduced a bill that would have set conservation targets for the agricultural industry. But the measure, which coincided with a debilitating drought that fallowed farmland and put thousands out of work, went nowhere.

It also faced opposition from many in the powerful farming community, who argued that a "one size fits all" conservation approach wouldn't work given vast differences in crop and soil types, hydrological zones and water delivery methods.

"Agricultural water use efficiency works differently from urban conservation - we don't have some low-flow shower head or toilet," said Mike Wade of the California Farm Water Coalition. "It's up to the irrigation district to designate feasible, cost-effective technology."

Instead, authors of the current legislative package, including Feuer, focused on rectifying some of the gaps in state water law.

For one, the measures require agricultural water suppliers to track the amount of water they deliver to their customers - a function not stipulated now.

Farmers are being asked to devise plans for potential ways to save water - which they may or may not put into practice.

The new laws don't penalize agricultural water suppliers for failing to craft the long-term water efficiency plans, but they do require water-related state money to be withheld if they don't comply.

Feuer admits that some of the provisions seem to tackle extremely basic problems. But the aims are pragmatic - from both hands-on and political perspectives.

"The bill is an incentive-based approach, but it's a strong one," Feuer said.

"I'm a big believer in legislation that's practical and can take effect," he added. "This year's bill goes as far as it can on agriculture (water use) to accomplish that."